build(ci): add dedicated preview config without optimize

[keldian]

An attempt to dodge the below error during preview builds (since enabled: !ENV [CI, false] does not make mkdocs ignore a missing plugin).

Run mkdocs build --clean
ERROR   -  Config value 'plugins': The "optimize" plugin is not installed

Aborted with a configuration error!
Error: Process completed with exit code 1.

[saltydk]

That is not a clean way of doing it, nor does it seem needed here.

[github-actions]

Deploying with ⚡ Cloudflare Pages

Latest commit:	e83c7f2664a9a0900bce532d97f94349c09876d3
Status:	❌  Build failed!
Preview URL:
Branch Preview URL:
Build logs:	View build logs

[keldian]

Aight.